A comprehensive genetic analysis of more than 200,000 men found that about 1 in 500 has an extra sex chromosome, most of which go undiagnosed. This is a much higher ratio than previously thought and appears to increase the risk of diseases such as diabetes and cardiovascular problems.
The new finding comes from data collected by the UK Biobank Project, which has comprehensively tracked the health and genetic data of half a million participants over the years. For this study, researchers from the Universities of Cambridge and Exeter analyzed genetic data from 200,000 men in the Biobank database, looking for a prevalence of extra sex chromosomes.
Sex chromosomes, marked as either X or Y, as the name suggests, are responsible for the differences between the biological sexes. Typically, females have two X chromosomes, while males usually have an X and a Y. But that’s not always the case.
In the new study, the scientists identified 213 men with an extra X and 143 men with an extra Y out of 200,000 men studied. Taking into account the general health of the biobank participants, the team calculated that about 500 men in the general population may have an extra sex chromosome, a much higher percentage than previously thought.
There were no signs of abnormalities in the medical records of most of the men in the study. Only 49 (or 23 percent) of the 213 with the added X were diagnosed with the condition, also known as Klinefelter syndrome. It usually manifests as delayed infertility or puberty and can then be detected and diagnosed, but often goes unnoticed. Only one in 143 men has now been diagnosed with the extra Y chromosome, as the condition has even fewer external symptoms.
The researchers then examined the health of these men and compared them to the rest of the biobank population. Men with XXY chromosomes had significantly lower blood testosterone levels and were three times more likely to have delayed puberty and four times more likely to be childless, suggesting infertility. On the other hand, men with XYY had normal reproductive function.
It was found that men who had extra copies of one of the chromosomes were at a higher risk of certain other disorders. Their risk of developing type 2 diabetes was three times higher than normal, six times higher for venous thrombosis, three times higher for pulmonary embolism and four times higher for chronic obstructive pulmonary disease.
The team says it’s uncertain why the extra chromosome would increase those risks, or why it was the same for both types. But further studies could help answer these questions and whether it makes sense to start screening people for extra chromosomes to prevent related diseases.
“Although males have an extra sex chromosome, very few are likely aware of it,” said study lead author Yajie Zhao. “This extra chromosome means they are at significantly higher risk of many common metabolic, vascular, and respiratory diseases — diseases that are preventable.”
The research results were published in the journal Genetics in Medicine.
Source: University of Cambridge